Manufacture of unstainable irons and steels



Patented June 1, 1926;

UNiTED STATES 1,586,592 PATENT OFFICE.

RONALD WILD, OF HOLMESFIELD, ENGLAND, ASSIGNOR, BY MESNE ASSIGNMENTS, TO RUSTLES$ IRON CORPORATION OF AMERICA, A CORPORATION OF MARYLAND.

MANUFACTURE OF UNSTAINABLE IRONS AND STEELS.

li'e Drawing. Original application flied February 5, 1923, Seria1 No. 617,172, and in Great Britain March 1, 1922;. Divided and this application filed May 4, 1928. Serial No. 636,758.

The present invention is for improvements in or relating to the manufacture of chrome-irons and chrome-steels of the class known commercially as stainless or unstainable iron and steel, described and claimed in my co-pending application Serial No. 617,172, filed Feb. 5, 1923, of which this application is a division.

In the manufacture of these steels and irons the alloy ferro-chrome is employed.

For the production of unstainable steels this alloy may contain a substantial proportion of carbon, say, 2 per cent or more, but for making unstainable chrome-irons it is the practice to use the grade of ferrochrome known ascarbon-fr ee, i. e. ferrochrome of a carbon content not exceeding 0.10 per cent. As the carbon-free alloy as ordinarily obtainable is comparatively costly, the manufacture therefrom of stainless iron is correspondingly expensive and the use of the latter is practically restricted to articles of high or relatively high price.

Ferro-chrome is usually prepared by reduction of chromite. This reductioninay be effected with a silicon-reducer and silicon and certain silicides have been proposed for this purpose. It has also been proposed to obtain appropriately low-carbon ferrochrome for the manufacture of unstainablemetal by submitting a crude ferro-chrome in the molten state to an oxidizing blow, but our experience is that this process of decarbonization of an iron-chromium alloy of high-chromium content is commercially uneconomical by reason of the high loss of chromium through oxidation. The loss is specially high when the attempt is made to eliminate carbon bythese means, while in the case of a silicon-containing ferrochrome prepared as aforesaid, where it is practically only a question of removing silicon, the loss of chromium may also'be such as to constitute a serious item 1n the production costs. The expense involved in the manufacture of high grade ferro-chrome is the main cause for the comparatively high price, and consequently of the relatively restricted field of application, of stainless metal.

The present invention has for its purpose to provide an improved and simplified process for the manufacture of stainless metal whereby the aforesaid difiiculties and manufacturing expenses may be reduced.

According to this invention, a molten crude ferro-chrome is admixed with molten oxidizable impurity whlch is present in sufficient quantity as to give, on admixture with the iron or steel, an excess over that permissible in a finished unstainable metal which is to possess deformable properties; This excess is then removed by the blow, which may be continued to any desired further reduction of thesilicon content.

The iron or steel bath is preferably substantially free from, or of low content in oxidizable impurities, such as carbon and silicon, and may advantageously contain oxygen or oxides- (for example, the bath may be provided by recently blown Bessemer metal) for the purpose of reducing, by a preliminary oxidation as well as by dilution, the quantity of the-impurities introduced by the crude ferro-chrome.

The crude ferro-chrome may be produced by reduction of a reducible compound of chromium in presence of iron (for instance, by reduction of an oxidized iron-chromium compound such as chromite) with approximately the equivalent of a substantially carbon-free or ow-carbon silicon-reducer, for the purpose of obtaining a. low-carbon ferro-chrome and consequently a crude unstainable metal therefrom which is free or. substantially free from excess carbon, andis practically associated only with excess of a foreign element, namely, silicon, which is more readily and economically removed than carbon by an oxidizing blow.

In the preferred mode of operation of the invention the low-carbon silicon-containing ferro-chrome is. produced in situ,.by effecting said reduction with the silicon-reducer within the bath of iron or steel, and I generally prefer tofollow this procedure than the alternative of first preparing the low-carbon ferro-chrome and then admixing it with the molten ironor steel.

By the expression low-carbon is meant tion is reduced, both by reason of the comparatively short time required for removing silicon and by the relatively low propordeformable, that is to say,

tionof chromium the dilutionwhich eration. Moreover, the presence in the or unstainable metal of a comparatively high proportion of silicon raises the temperature of the molten mass during the blow, and this condition also tends to reduce the degree of oxidation of the chromium.

The preferred silicon-reducer ferrosilicon, which may advantageously be a ferro-silicon of high-silicon content, for instance, 80 per cent silicon or more.

' The carbon content of the ferro-silicon or the like should be known so that allowance may be made therefor in preparin according to the nature of the fi desired.

By operating according to the present invention, it is readily possible to obtain an unstainable chrome-iron or chrome-steel of low average ties, such as carbon and silicon, and

nal metal properly possessing the physical attributes necessary to enable the metal to be deformed or shaped by forging, rolling, drop-stamping, cold-drawing or pressing, and like processes commonly emplo ed in the manufacture of objects for wbliich metal of this unstainable type is suita e.

By a low average content in oxidizable impurities is meant a content in carbon such, as is known in the art, is insufiicient deleteriously to effect the unstainable properties of the metal, and a content in silicon not exceeding about 1 per cent. By the aforesaid reduction with a low-carbon silicon-reducer followed by blowing of the crude unstainable metal, however, a product of a considerably lower content in silicon than 1 per cent may be readily obtained.

In the case of the preparation of unstainable steel, the necessary proportion of carbon may be supplied at any convenient stage of the process by the addition of suitable carbon-containing materials as are known in the art, for example, either-by way of the metal employed for the dilution bath or present consequent upon precedes the blowing op u eto tapping or to b the bath,

content in oxidizable impuriby addition to the latter or the dilution product of the requisite uantity of pig-iron, or by coal or charcoal added to the metal in the ladle.

The invention may be carried out in any available furnace provided that the latter is capable of maintaining complete fusion of the materials throughout the operations and of permitting the finished roduct to be poured or tapped. External heating may be applied in order to maintain the requisite high temperature throughout the reduction, or at any stage during or subsequent to the passage of the blow. An electric furnace, for instance, of the Heroult or Snyder type, may conveniently be employed.

Advantageously a suitable deoxidizer is introduced into t lye dilution product prior owing. For example, the metal to be blown may contain from about 1 up to 2.5 per cent of manganese. The manganese may be introduced by effecting reduction of the chromium compound in presence of the manganese, or of a, reducible manganese compound.

- The use of manganese in quantity in excess of a minimum of 2 per cent, for the protection of the chromium component of crude unstainable metal during blowing is described and claimed in my specification, Serial No. 617,171.

The following examples are illustrative of the invention:

Example I.

A ferro-chrome was first prepared by. reducing a crushed and washed chromite with the calculated quantity of a high-silicon fer-' ro-silicon, whereby there was obtained an alloy containing 0.20 per cent of carbon and ,12 per cent of silicon. To this alloy was added ferro-manganese containing 80 per cent manganese and 7 percent carbon in such proportion as to give a metal containmg Per cent. Chromium 58.50 Manganese 8.00 Silicon 10.90 Carbon 0.88

Per cent. Chromium 11.70 Manganese 1.60 Silicon 2.18 Carbon 0.18

The contents of the converter was thensubmitted to an oxidizing blow, the purified metal assaying as follows 2- Emample H.

To a bath of 5% cwts. of iron and steel scrap, containing 0.07 per cent of carbon, were added 71 lbs. of ferro-silicon, assaying I 83 per cent of silicon, equivalent to 212 lbs.

of chromium sesquioxide. To this ferrosilicon-contalning bath were then added 111 successive charges 400 lbs. of chrome-iron ore, containin 211 lbs. of chromium sesquioxide, toget er with 35 lbs. of limestone and 24 lbs. of fluorspar. At this stage the molten metal corresponded to approx1mate by 5% cwts. of an alloy steel of the following composition Per cent.

' Chromium 14.50 Silicon 1.33 Carbon 0.11

This metal was then submitted to an oxidizin blow, and then after-the addition of 7 1 set ferro-manganese (80 per cent manganese) and the'usua-l small percentage of aluminium, and tapping, assayed as follows Per cent.

Chromium 11.60 Silicon 0.21 Manganese 1 0.35 Carbon 0.17

The yield of unstainable metal so obtained was 5 cwt. 1 qr. 20 lbs. the loss of chromium due to oxidation by the blow being approximately 20 er cent, of the metal present at the conclusion of the reduction stage.

The above examples aregiven for illustrative purposes and not by way of limitation. For instance, the invention is not restricted to the production of unstainable metal containing the percentage of chromium given, but may be applied to any metal of this class in which the 'roportion of chromium is suflicient to confer the property known as stainless or unstainable.

Iron and steel free fromundesirable impurities and of low and known carbon content are readily and cheaply obtainable, while silicon-reducers, such, for instance, as ferro-silicon, of low-carbon content may also be obtained without difficulty. In contradistinction to the manufacture of high-grade ferro-chrome as ordinarily employed, the preparation of ferro-chrome containing silicon is both cheaper and more readily carried out. As previously stated, silicon is more readily removed than carbon by an oxidizing blow, and, as is known, its presence in molten metal facilitates the blowing operation, and when the latter is carried out upon a metal of comparatively low chromium content, such as unstainable metal, the loss of chromium through oxidation may be maintamed within practicable limits. The present invention therefore provides through this combination of conditions a sim lified process for the manufacture of unstainable' chrome-irons and chrome-steels with improved economy and expedition.

' The expression unstainable metal as used in the claims of this specification means an iron-chromium alloy wherein the chromi um is the minor metallic component and in such proportion as to confer unstainable properties, and of such a content in carbon as, consistently with the retention of unstainable properties, corresponds to an unstainable alloy of the class either of chromeironor chrome-steel. Similarly, a ferrous bath means a bath composed of molten iron or steel, or one compounded of the two together.

I claim 1. The manufacture of 'unstainable metal which comprises diluting with molten iron of low-carbon content, the iron-chromium product of reducing a substantially noncarboniferous compound of iron and chromium with a low-carbon silicon reducer, so as to obtain a dilution product in the form of a low-carbon silicon-contaminated initial alloy containing iron and chromium in the relative proportions in which these metals are present in unstainable metal and uncontaminated with carbon, phosphorous and sulphur beyond the tolerance limits for these impurities in finished unstainable metal, and then submitting the dilution product to purification by an oxidizing blow.

2. The manufacture of unstainable metal which comprises diluting with molten iron of low-carbon content, the iron-chromium product of reducing a substantially noncarboniferous compound of iron and chromium with a low-carbon silicon reducer, so as to obtain a. dilution product in the form of a low-carbon silicon-contaminated initial alloy containing iron and chromium in the relative proportions in which these metals are present in unstainable metal and uncontaminated with carbon phosphorous and sulphur beyond the tolerance limits for these impurities in finished unstainable metal, and then submitting the dilution product to purification by an oxidizing blow under application of external heat. v

' 3. The manufacture of unstainable metal which comprises diluting with molten iron of low-carbon content, the iron-chromium product of reducing a substantially noncarboniferous compound of iron and chromium with a low-carbon silicon reducer, so as toobtain a dilution product in the form of a low-carbon silicon-contaminated initial alloy containing iron and chromium in the relative proportions in which these metals are present in unstainable metal and uncontaminated with carbon phosphorous and sulphur beyond the tolerance limits for these impurities in finished unstainable metal, and then submitting the dilution product to purification by an oxidizing blow in presence of manganese up to approximately 2.5% of said initial alloy.

4. The manufacture of unstainable metal which comprises diluting with molten iron of low-carbon content, the iron-chromium product of reducing a. substantially noncarboniferous compound of iron and chromium with a low-carbon silicon reducer, so as to obtain a dilution product in the form of a low-carbon silicon-contaminated initial alloy of iron and chromium having a chromium content of substantially between 9 and 16% and uncontaminated with carbon phosphorous and sulphur beyond the tolerance limits for these impurities in finished unstainable metal, and then submitting the dilution product to purification by an oxidizing blow.

5. The manufacture of unstainable metalwhich comprises diluting with molten iron of low-carbon content; the ironchromium product of reducing a substantially non-carboniferous compound of iron and chromium with a low-carbon silicon reducer, so as to obtain a dilution product in the form of a low-carbon silicon-contami nated initial alloy of iron and chromium having a chromium content of substantially between 9 and 16% and uncontaminated with carbon phosphorous and sulphur beyond the tolerance limits for these impurities in finished unstainable metal, and then submitting the dilution product to purification by an oxidizing blow in presence of manganese up to approximately 2.5% of said initial alloy.

6. The manufacture of unstainable metal which comprises reducing within a molten ferrous bath of low-carbon content, by means of a low-carbon silicon-reducer, a reducible substantially non-carboniferous compound of iron and chromium, so as to obtain a lowcarbon silicon-contamin ated initial alloy containing iron and chromium in the relative proportions in which these metals are present in unstainable metal and uncontaminated with carbon phosphorous and sulphur beyond the tolerance limits for these impurities in finished unstainable metal, and then submitting said molten alloy to purification by an oxidizing blow.

7. The manufacture of unstainable metal which comprises reducing within a molten ferrous bath of low-carbon content, by means of a low-carbon ferro-silicon, a reducible substantially non-carboniferous compound of iron and chromium, so as to obtain a lowcarbon silicon-contaminated initial alloy containing iron and chromium in the relacompound of iron and chromium, so as to obtain a low-carbon silicon-contaminated initial alloy containing iron and chromium in the relativeproportions in which these metals are present in unstainable metal and uncontaminated with carbon phosphorous and sulphur beyond the tolerance limits for these impurities in finished unstainable metal, and then submitting said molten alloy to purification by an oxidizing-blow.

9. The manufacture of unstainable metal which comprises reducing chromite within a molten ferrous bath of low-carbon content, by means of a low-carbon silicon-reducer, so as to obtain a low-carbon silicon-contaminated initial alloy containing iron and chromium in the relative proportions in which these metals are present in unstainable metal and uncontaminated with carbon phosphorous and sulphur beyond the tolerance limits for these impurities in finished unstainable metal, and then submitting said molten alloy to purification by an oxidizing blow.

10. 'Ihe manufacture of unstainable metal which comprises reducin chromite within a molten'ferrous bath ofTow-carbon content, by means of a low-carbon ferro-silicon, so as to obtain a low-carbon silicon-contaminated initial alloy containing iron and chromium in the relative proportions in which these metals are present in unstainable metal and uncontaminatadwith carbon phosphorous reducible substantially non-carboniferous' compound of iron and chromium, so as to obtain a low-carbon silicon-contaminated initial alloy containing iron and chromium in the relative proportions in which these metals are present in unstainable metal and uncontaminated with carbon phosphorous and sulphur beyond the tolerance limits for these impurities in finished unstainable metal, and then submitting said molten alloy to purification by an oxidizing blow in the presence of substantially 1 to 2.5% of manganese.

12. The manufacture of unstainable metal which comprises reducing chromite within a molten ferrous bath of low-carbon content, by means of low-carbon ferro-silicon, so as to obtain a low-carbon silicon-contaminatedcarboniferous compound of iron and chro mium with'a low-carbon silicon reducer, so as to obtain a dilution product in the form of a low-carbon silicon-contaminated initial alloy containing iron and chromium in the relative proportions in which these metals are present in unstainable metal and uncontammated with carbon phosphorous and sulhur beyond the tolerance limits for these mpurities in finished unstainable metal, and

then blowin the dilution product until the content in silicon is reduced below 0.5%.

14. The manufacture of-unstainable metal which comprises reducing within a molten ferrous bath of low-carbon content, by means of a low-carbon silicon-reducer, a reducible substantially non-carboniferous compound of iron and chromium, so as to obtain a low carbon silicon-contaminated initial alloy containing iron and chromium in the relative proportions in which these metals are present in unstainable metal anduncontaminated with carbon phosphorous and sulphur beyond the tolerance limits for these impurities in finished unstainable metal, and then blowing the molten alloy until the content in silicon'is reduced below 0.5%. I

15. The manufacture of unstainablemetal which comprises diluting with molten .rc-

cently blown Bessemer metal, the iron-chromium product of reducing substantially 'non-.

carbonaceous compound of iron and chro mium with a low-carbon silicon reducer, so as to obtain a dilution product'in the form of a low-carbon silicon-contaminated initial alloy containing iron and chromium in the relative proportions in which these metals are presentin unstainable metal and uncontaminated with carbon phosphorous and sulphur beyond the tolerance limits for these impurities in finished unstainablemetal, and then submitting the dilution product to purification by an oxidizing blow.

16. They manufacture of unstainable metal which comprises diluting with molten recently blown Bessemer metal from which the Bessemeri zing slag has been removed, the iron-chromium product of reducing a substantially non-Carboniferous compound of iron and chromium with a low-carbon silicon reducer, so as to obtain a dilution prod not in the form of a low-carbon silicon-contaminated initial alloy containing iron and chromium in the relative proportions in WhlCh these metals are present 1n unstainable metal and uncontaminated with carbon phosphorous and sulphur beyond the tolerance limits for these impurities in finished unstainable metal, and thensubmitting the dilution product to purification by an oxidizing blow.

In testimony whereof I afiix my signature.

RONALD WILD. 

